A TV receiver of an extremely thin thickness, such as one employing a liquid crystal display (LCD) or a plasma display panel (PDP), has been developed and put to practical use to take the place of a TV receiver employing a cathode ray tube (CRT) which has long been used since the start of TV broadcasting. In particular, a color liquid crystal display apparatus employing a color liquid crystal display panel is expected to become popular at a high pace because it permits driving with low power consumption and the large-sized color liquid crystal display panel has become less expensive.
As for the color liquid crystal display apparatus, the backlight system, in which a transmissive color liquid crystal display panel is illuminated from its backside with a backlight device to display a color picture, is in the mainstream. The light source, preferentially used for the backlight device, is a CCFL (Cold Cathode Fluorescent Lamp), emitting white light using a fluorescent tube.
In general, in a transmissive color liquid crystal display apparatus, a color filter, employing a tristimulus filter of spectral characteristics, shown for example in FIG. 1, made up of a blue filter CFB0 (460 nm), a green filter CFG0 (530 nm) and a red filter CFR0 (685 nm), where the numbers entered in parentheses denote the peak transmission wavelength of each filter, is provided from one pixel of the color liquid crystal display panel to another.
On the other hand, the white light, emitted by a three-wavelength CCFL, used as a light source for a backlight device of the color liquid crystal display apparatus, has a spectrum shown in FIG. 2. That is, the white light emitted by the CCFL contains light of different intensities in a variety of wavelengths.
Hence, the color reproduced by the combination of the backlight device, having such CCFL, emitting the light of three wavelength ranges, as light source, and the color liquid crystal display panel, having the color filter, described above, is rather poor in color purity.
FIG. 3 shows the color reproducing range of the color liquid crystal display apparatus, including the backlight device, having the above-described tristimulus CCFL as a light source. Specifically, FIG. 3 depicts an xy chromaticity diagram of the XYZ color system, as prescribed by the Commission Internationale de l'Eclairage (CIE).
As may be seen from FIG. 3, the color reproducing range of the color liquid crystal display apparatus, having the backlight device, employing the CCFL as light source, is narrower than the color reproducing range provided for by the standard of the NTSC (National Television System Committee) system accepted as the color television broadcasting system. That is, the first-stated color reproducing range may not be said to cope sufficiently with the current television broadcasting.
On the other hand, there is a fear that the CCFL, containing mercury in the phosphorescent tube, may have an ill effect on the environment. Hence, a demand is raised for a light source which may be used in substitution for the CCFL as a light source of the backlight device. With the development of the blue light emitting diode, the light emitting diodes, emitting light of three prime colors, namely red light, green light and blue light, are now in order. Thus, with the use of the light emitting diodes as light source for the backlight device, the color light obtained by the color liquid crystal display panel may be improved in color purity, and hence it may be expected that the color reproducing range may be made as broad as or even broader than the color reproducing range provided for by the NTSC system.
However, there is a problem that the color reproducing range of the color liquid crystal display apparatus, employing light emitting diodes as light source, is not as yet broad enough to satisfy the color reproducing range provided by the NTSC system.